Porous particles constructed from electrochemically etched porous materials, such as silicon, have widespread application in optoelectronics, chemical and biological sensors, high-throughput screening, and drug delivery applications. These porous particles are especially advantageous because of the relative ease with which the optical properties, pore size, and surface chemistry can be manipulated. Moreover, position, width, and intensity of spectral reflectivity peaks may be controlled by the current density waveform and solution composition used in the electrochemical etch, thus rendering possible the preparation of films of porous particles that display any color within the visible light band with high color saturation, which is a desirable feature for information displays.
A well-appreciated need for labeling exists in society. Labeling is a fundamental basis for tracking and identifying. Encoding can be used as a form of labeling understood by persons or equipment, as in the case of bar coding. At the microscale, however, labeling/encoding itself becomes difficult.
Porous particles and films constructed from electrochemically etched porous materials have provided powerful methods for labeling and encoding. Porous particles and films and methods using such are disclosed in 1) U.S. Published Patent Application 20050042764, entitled “Optically encoded particles” to Sailor et al., published Feb. 24, 2005; 2) U.S. Published Patent Application 20050009374, entitled “Direct patterning of silicon by photoelectrochemical etching”, to Gao, et al., published Jan. 13, 2005, now U.S. Pat. No. 7,433,811, issued Oct. 7, 2008; 3) U.S. Published Patent Application 20030146109 entitled “Porous thin film time-varying reflectivity analysis of samples,” to Sailor, et al. published Aug. 7, 2003, now U.S. Pat. No. 7,042,570, issued May 9, 2006; 4) PCT Application PCT/US04/043001, entitled “Optically encoded particles, system and high throughput screening, to Sailor et al, filed Dec. 21, 2004, now U.S. Publication No. US-2007-0148695-A1, published Jun. 28, 2007; 5) PCT Application PCT/US04/042997, entitled “Optically encoded particles with grey scale spectra,” to Sailor et al, filed Dec. 21, 2004, now U.S. Publication No. US-2007-0051815-A1, published Mar. 8, 2007; and 6) PCT Application PCT/US04/26572, entitled, “Photonic Sensor Particles and Fabrication Methods”, to Sailor, et al filed Aug. 13, 2004, now U.S. Pat. No. 7,167,605, issued Jan. 23, 2007.